X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FBranchFolding.cpp;h=7f98df0d22ea4318f0bc4256771df7de03717975;hb=98ec91ea80e042907aac8d3cbd9614d29f6cba45;hp=583009c74a3b6375175801a9eab558478ff0f642;hpb=dc54d317e7a381ef8e4aca80d54ad1466bb85dda;p=oota-llvm.git diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp index 583009c74a3..7f98df0d22e 100644 --- a/lib/CodeGen/BranchFolding.cpp +++ b/lib/CodeGen/BranchFolding.cpp @@ -17,6 +17,8 @@ //===----------------------------------------------------------------------===// #define DEBUG_TYPE "branchfolding" +#include "BranchFolding.h" +#include "llvm/Function.h" #include "llvm/CodeGen/Passes.h" #include "llvm/CodeGen/MachineModuleInfo.h" #include "llvm/CodeGen/MachineFunctionPass.h" @@ -27,7 +29,10 @@ #include "llvm/Target/TargetRegisterInfo.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/raw_ostream.h" #include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/SetVector.h" #include "llvm/ADT/Statistic.h" #include "llvm/ADT/STLExtras.h" #include @@ -36,95 +41,70 @@ using namespace llvm; STATISTIC(NumDeadBlocks, "Number of dead blocks removed"); STATISTIC(NumBranchOpts, "Number of branches optimized"); STATISTIC(NumTailMerge , "Number of block tails merged"); -static cl::opt FlagEnableTailMerge("enable-tail-merge", + +static cl::opt FlagEnableTailMerge("enable-tail-merge", cl::init(cl::BOU_UNSET), cl::Hidden); + // Throttle for huge numbers of predecessors (compile speed problems) static cl::opt -TailMergeThreshold("tail-merge-threshold", +TailMergeThreshold("tail-merge-threshold", cl::desc("Max number of predecessors to consider tail merging"), cl::init(150), cl::Hidden); +// Heuristic for tail merging (and, inversely, tail duplication). +// TODO: This should be replaced with a target query. +static cl::opt +TailMergeSize("tail-merge-size", + cl::desc("Min number of instructions to consider tail merging"), + cl::init(3), cl::Hidden); + namespace { - struct VISIBILITY_HIDDEN BranchFolder : public MachineFunctionPass { + /// BranchFolderPass - Wrap branch folder in a machine function pass. + class BranchFolderPass : public MachineFunctionPass, + public BranchFolder { + public: static char ID; - explicit BranchFolder(bool defaultEnableTailMerge) : - MachineFunctionPass(&ID) { - switch (FlagEnableTailMerge) { - case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break; - case cl::BOU_TRUE: EnableTailMerge = true; break; - case cl::BOU_FALSE: EnableTailMerge = false; break; - } - } + explicit BranchFolderPass(bool defaultEnableTailMerge) + : MachineFunctionPass(&ID), BranchFolder(defaultEnableTailMerge) {} virtual bool runOnMachineFunction(MachineFunction &MF); virtual const char *getPassName() const { return "Control Flow Optimizer"; } - const TargetInstrInfo *TII; - MachineModuleInfo *MMI; - bool MadeChange; - private: - // Tail Merging. - bool EnableTailMerge; - bool TailMergeBlocks(MachineFunction &MF); - bool TryMergeBlocks(MachineBasicBlock* SuccBB, - MachineBasicBlock* PredBB); - void ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst, - MachineBasicBlock *NewDest); - MachineBasicBlock *SplitMBBAt(MachineBasicBlock &CurMBB, - MachineBasicBlock::iterator BBI1); - unsigned ComputeSameTails(unsigned CurHash, unsigned minCommonTailLength); - void RemoveBlocksWithHash(unsigned CurHash, MachineBasicBlock* SuccBB, - MachineBasicBlock* PredBB); - unsigned CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB, - unsigned maxCommonTailLength); - - typedef std::pair MergePotentialsElt; - typedef std::vector::iterator MPIterator; - std::vector MergePotentials; - - typedef std::pair SameTailElt; - std::vector SameTails; - - const TargetRegisterInfo *RegInfo; - RegScavenger *RS; - // Branch optzn. - bool OptimizeBranches(MachineFunction &MF); - void OptimizeBlock(MachineBasicBlock *MBB); - void RemoveDeadBlock(MachineBasicBlock *MBB); - bool OptimizeImpDefsBlock(MachineBasicBlock *MBB); - - bool CanFallThrough(MachineBasicBlock *CurBB); - bool CanFallThrough(MachineBasicBlock *CurBB, bool BranchUnAnalyzable, - MachineBasicBlock *TBB, MachineBasicBlock *FBB, - const SmallVectorImpl &Cond); }; - char BranchFolder::ID = 0; } -FunctionPass *llvm::createBranchFoldingPass(bool DefaultEnableTailMerge) { - return new BranchFolder(DefaultEnableTailMerge); } +char BranchFolderPass::ID = 0; + +FunctionPass *llvm::createBranchFoldingPass(bool DefaultEnableTailMerge) { + return new BranchFolderPass(DefaultEnableTailMerge); +} + +bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) { + return OptimizeFunction(MF, + MF.getTarget().getInstrInfo(), + MF.getTarget().getRegisterInfo(), + getAnalysisIfAvailable()); +} + + +BranchFolder::BranchFolder(bool defaultEnableTailMerge) { + switch (FlagEnableTailMerge) { + case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break; + case cl::BOU_TRUE: EnableTailMerge = true; break; + case cl::BOU_FALSE: EnableTailMerge = false; break; + } +} /// RemoveDeadBlock - Remove the specified dead machine basic block from the /// function, updating the CFG. void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) { assert(MBB->pred_empty() && "MBB must be dead!"); - DOUT << "\nRemoving MBB: " << *MBB; - + DEBUG(dbgs() << "\nRemoving MBB: " << *MBB); + MachineFunction *MF = MBB->getParent(); // drop all successors. while (!MBB->succ_empty()) MBB->removeSuccessor(MBB->succ_end()-1); - - // If there are any labels in the basic block, unregister them from - // MachineModuleInfo. - if (MMI && !MBB->empty()) { - for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); - I != E; ++I) { - if (I->isLabel()) - // The label ID # is always operand #0, an immediate. - MMI->InvalidateLabel(I->getOperand(0).getImm()); - } - } - + // Remove the block. MF->erase(MBB); } @@ -142,11 +122,11 @@ bool BranchFolder::OptimizeImpDefsBlock(MachineBasicBlock *MBB) { SmallSet ImpDefRegs; MachineBasicBlock::iterator I = MBB->begin(); while (I != MBB->end()) { - if (I->getOpcode() != TargetInstrInfo::IMPLICIT_DEF) + if (!I->isImplicitDef()) break; unsigned Reg = I->getOperand(0).getReg(); ImpDefRegs.insert(Reg); - for (const unsigned *SubRegs = RegInfo->getSubRegisters(Reg); + for (const unsigned *SubRegs = TRI->getSubRegisters(Reg); unsigned SubReg = *SubRegs; ++SubRegs) ImpDefRegs.insert(SubReg); ++I; @@ -180,82 +160,71 @@ bool BranchFolder::OptimizeImpDefsBlock(MachineBasicBlock *MBB) { return true; } -bool BranchFolder::runOnMachineFunction(MachineFunction &MF) { - TII = MF.getTarget().getInstrInfo(); - if (!TII) return false; +/// OptimizeFunction - Perhaps branch folding, tail merging and other +/// CFG optimizations on the given function. +bool BranchFolder::OptimizeFunction(MachineFunction &MF, + const TargetInstrInfo *tii, + const TargetRegisterInfo *tri, + MachineModuleInfo *mmi) { + if (!tii) return false; - RegInfo = MF.getTarget().getRegisterInfo(); + TII = tii; + TRI = tri; + MMI = mmi; + + RS = TRI->requiresRegisterScavenging(MF) ? new RegScavenger() : NULL; // Fix CFG. The later algorithms expect it to be right. - bool EverMadeChange = false; + bool MadeChange = false; for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; I++) { MachineBasicBlock *MBB = I, *TBB = 0, *FBB = 0; SmallVector Cond; if (!TII->AnalyzeBranch(*MBB, TBB, FBB, Cond, true)) - EverMadeChange |= MBB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty()); - EverMadeChange |= OptimizeImpDefsBlock(MBB); + MadeChange |= MBB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty()); + MadeChange |= OptimizeImpDefsBlock(MBB); } - RS = RegInfo->requiresRegisterScavenging(MF) ? new RegScavenger() : NULL; - - MMI = getAnalysisIfAvailable(); - bool MadeChangeThisIteration = true; while (MadeChangeThisIteration) { MadeChangeThisIteration = false; MadeChangeThisIteration |= TailMergeBlocks(MF); MadeChangeThisIteration |= OptimizeBranches(MF); - EverMadeChange |= MadeChangeThisIteration; + MadeChange |= MadeChangeThisIteration; } - // See if any jump tables have become mergable or dead as the code generator + // See if any jump tables have become dead as the code generator // did its thing. MachineJumpTableInfo *JTI = MF.getJumpTableInfo(); - const std::vector &JTs = JTI->getJumpTables(); - if (!JTs.empty()) { - // Figure out how these jump tables should be merged. - std::vector JTMapping; - JTMapping.reserve(JTs.size()); - - // We always keep the 0th jump table. - JTMapping.push_back(0); - - // Scan the jump tables, seeing if there are any duplicates. Note that this - // is N^2, which should be fixed someday. - for (unsigned i = 1, e = JTs.size(); i != e; ++i) - JTMapping.push_back(JTI->getJumpTableIndex(JTs[i].MBBs)); - - // If a jump table was merge with another one, walk the function rewriting - // references to jump tables to reference the new JT ID's. Keep track of - // whether we see a jump table idx, if not, we can delete the JT. - BitVector JTIsLive(JTs.size()); - for (MachineFunction::iterator BB = MF.begin(), E = MF.end(); - BB != E; ++BB) { - for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); - I != E; ++I) - for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) { - MachineOperand &Op = I->getOperand(op); - if (!Op.isJTI()) continue; - unsigned NewIdx = JTMapping[Op.getIndex()]; - Op.setIndex(NewIdx); - - // Remember that this JT is live. - JTIsLive.set(NewIdx); - } - } - - // Finally, remove dead jump tables. This happens either because the - // indirect jump was unreachable (and thus deleted) or because the jump - // table was merged with some other one. - for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i) - if (!JTIsLive.test(i)) { - JTI->RemoveJumpTable(i); - EverMadeChange = true; - } + if (JTI == 0) { + delete RS; + return MadeChange; } + // Walk the function to find jump tables that are live. + BitVector JTIsLive(JTI->getJumpTables().size()); + for (MachineFunction::iterator BB = MF.begin(), E = MF.end(); + BB != E; ++BB) { + for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); + I != E; ++I) + for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) { + MachineOperand &Op = I->getOperand(op); + if (!Op.isJTI()) continue; + + // Remember that this JT is live. + JTIsLive.set(Op.getIndex()); + } + } + + // Finally, remove dead jump tables. This happens when the + // indirect jump was unreachable (and thus deleted). + for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i) + if (!JTIsLive.test(i)) { + JTI->RemoveJumpTable(i); + MadeChange = true; + } + delete RS; - return EverMadeChange; + return MadeChange; } //===----------------------------------------------------------------------===// @@ -267,7 +236,7 @@ static unsigned HashMachineInstr(const MachineInstr *MI) { unsigned Hash = MI->getOpcode(); for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { const MachineOperand &Op = MI->getOperand(i); - + // Merge in bits from the operand if easy. unsigned OperandHash = 0; switch (Op.getType()) { @@ -289,35 +258,27 @@ static unsigned HashMachineInstr(const MachineInstr *MI) { break; default: break; } - + Hash += ((OperandHash << 3) | Op.getType()) << (i&31); } return Hash; } -/// HashEndOfMBB - Hash the last few instructions in the MBB. For blocks -/// with no successors, we hash two instructions, because cross-jumping -/// only saves code when at least two instructions are removed (since a -/// branch must be inserted). For blocks with a successor, one of the -/// two blocks to be tail-merged will end with a branch already, so -/// it gains to cross-jump even for one instruction. - -static unsigned HashEndOfMBB(const MachineBasicBlock *MBB, - unsigned minCommonTailLength) { +/// HashEndOfMBB - Hash the last instruction in the MBB. +static unsigned HashEndOfMBB(const MachineBasicBlock *MBB) { MachineBasicBlock::const_iterator I = MBB->end(); if (I == MBB->begin()) return 0; // Empty MBB. - - --I; - unsigned Hash = HashMachineInstr(I); - - if (I == MBB->begin() || minCommonTailLength == 1) - return Hash; // Single instr MBB. - + --I; - // Hash in the second-to-last instruction. - Hash ^= HashMachineInstr(I) << 2; - return Hash; + // Skip debug info so it will not affect codegen. + while (I->isDebugValue()) { + if (I==MBB->begin()) + return 0; // MBB empty except for debug info. + --I; + } + + return HashMachineInstr(I); } /// ComputeCommonTailLength - Given two machine basic blocks, compute the number @@ -329,43 +290,78 @@ static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1, MachineBasicBlock::iterator &I2) { I1 = MBB1->end(); I2 = MBB2->end(); - + unsigned TailLen = 0; while (I1 != MBB1->begin() && I2 != MBB2->begin()) { --I1; --I2; - if (!I1->isIdenticalTo(I2) || + // Skip debugging pseudos; necessary to avoid changing the code. + while (I1->isDebugValue()) { + if (I1==MBB1->begin()) { + while (I2->isDebugValue()) { + if (I2==MBB2->begin()) + // I1==DBG at begin; I2==DBG at begin + return TailLen; + --I2; + } + ++I2; + // I1==DBG at begin; I2==non-DBG, or first of DBGs not at begin + return TailLen; + } + --I1; + } + // I1==first (untested) non-DBG preceding known match + while (I2->isDebugValue()) { + if (I2==MBB2->begin()) { + ++I1; + // I1==non-DBG, or first of DBGs not at begin; I2==DBG at begin + return TailLen; + } + --I2; + } + // I1, I2==first (untested) non-DBGs preceding known match + if (!I1->isIdenticalTo(I2) || // FIXME: This check is dubious. It's used to get around a problem where // people incorrectly expect inline asm directives to remain in the same // relative order. This is untenable because normal compiler // optimizations (like this one) may reorder and/or merge these // directives. - I1->getOpcode() == TargetInstrInfo::INLINEASM) { + I1->isInlineAsm()) { ++I1; ++I2; break; } ++TailLen; } + // Back past possible debugging pseudos at beginning of block. This matters + // when one block differs from the other only by whether debugging pseudos + // are present at the beginning. (This way, the various checks later for + // I1==MBB1->begin() work as expected.) + if (I1 == MBB1->begin() && I2 != MBB2->begin()) { + --I2; + while (I2->isDebugValue()) { + if (I2 == MBB2->begin()) { + return TailLen; + } + --I2; + } + ++I2; + } + if (I2 == MBB2->begin() && I1 != MBB1->begin()) { + --I1; + while (I1->isDebugValue()) { + if (I1 == MBB1->begin()) + return TailLen; + --I1; + } + ++I1; + } return TailLen; } /// ReplaceTailWithBranchTo - Delete the instruction OldInst and everything -/// after it, replacing it with an unconditional branch to NewDest. This -/// returns true if OldInst's block is modified, false if NewDest is modified. +/// after it, replacing it with an unconditional branch to NewDest. void BranchFolder::ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst, MachineBasicBlock *NewDest) { - MachineBasicBlock *OldBB = OldInst->getParent(); - - // Remove all the old successors of OldBB from the CFG. - while (!OldBB->succ_empty()) - OldBB->removeSuccessor(OldBB->succ_begin()); - - // Remove all the dead instructions from the end of OldBB. - OldBB->erase(OldInst, OldBB->end()); - - // If OldBB isn't immediately before OldBB, insert a branch to it. - if (++MachineFunction::iterator(OldBB) != MachineFunction::iterator(NewDest)) - TII->InsertBranch(*OldBB, NewDest, 0, SmallVector()); - OldBB->addSuccessor(NewDest); + TII->ReplaceTailWithBranchTo(OldInst, NewDest); ++NumTailMerge; } @@ -374,6 +370,9 @@ void BranchFolder::ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst, /// iterator. This returns the new MBB. MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB, MachineBasicBlock::iterator BBI1) { + if (!TII->isLegalToSplitMBBAt(CurMBB, BBI1)) + return 0; + MachineFunction &MF = *CurMBB.getParent(); // Create the fall-through block. @@ -383,10 +382,10 @@ MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB, // Move all the successors of this block to the specified block. NewMBB->transferSuccessors(&CurMBB); - + // Add an edge from CurMBB to NewMBB for the fall-through. CurMBB.addSuccessor(NewMBB); - + // Splice the code over. NewMBB->splice(NewMBB->end(), &CurMBB, BBI1, CurMBB.end()); @@ -395,9 +394,9 @@ MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB, RS->enterBasicBlock(&CurMBB); if (!CurMBB.empty()) RS->forward(prior(CurMBB.end())); - BitVector RegsLiveAtExit(RegInfo->getNumRegs()); + BitVector RegsLiveAtExit(TRI->getNumRegs()); RS->getRegsUsed(RegsLiveAtExit, false); - for (unsigned int i=0, e=RegInfo->getNumRegs(); i!=e; i++) + for (unsigned int i = 0, e = TRI->getNumRegs(); i != e; i++) if (RegsLiveAtExit[i]) NewMBB->addLiveIn(i); } @@ -411,6 +410,8 @@ static unsigned EstimateRuntime(MachineBasicBlock::iterator I, MachineBasicBlock::iterator E) { unsigned Time = 0; for (; I != E; ++I) { + if (I->isDebugValue()) + continue; const TargetInstrDesc &TID = I->getDesc(); if (TID.isCall()) Time += 10; @@ -426,95 +427,167 @@ static unsigned EstimateRuntime(MachineBasicBlock::iterator I, // branches temporarily for tail merging). In the case where CurMBB ends // with a conditional branch to the next block, optimize by reversing the // test and conditionally branching to SuccMBB instead. - -static void FixTail(MachineBasicBlock* CurMBB, MachineBasicBlock *SuccBB, +static void FixTail(MachineBasicBlock *CurMBB, MachineBasicBlock *SuccBB, const TargetInstrInfo *TII) { MachineFunction *MF = CurMBB->getParent(); - MachineFunction::iterator I = next(MachineFunction::iterator(CurMBB)); + MachineFunction::iterator I = llvm::next(MachineFunction::iterator(CurMBB)); MachineBasicBlock *TBB = 0, *FBB = 0; SmallVector Cond; + DebugLoc dl; // FIXME: this is nowhere if (I != MF->end() && !TII->AnalyzeBranch(*CurMBB, TBB, FBB, Cond, true)) { MachineBasicBlock *NextBB = I; if (TBB == NextBB && !Cond.empty() && !FBB) { if (!TII->ReverseBranchCondition(Cond)) { TII->RemoveBranch(*CurMBB); - TII->InsertBranch(*CurMBB, SuccBB, NULL, Cond); + TII->InsertBranch(*CurMBB, SuccBB, NULL, Cond, dl); return; } } } - TII->InsertBranch(*CurMBB, SuccBB, NULL, SmallVector()); + TII->InsertBranch(*CurMBB, SuccBB, NULL, + SmallVector(), dl); } -static bool MergeCompare(const std::pair &p, - const std::pair &q) { - if (p.first < q.first) - return true; - else if (p.first > q.first) - return false; - else if (p.second->getNumber() < q.second->getNumber()) - return true; - else if (p.second->getNumber() > q.second->getNumber()) - return false; - else { - // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing - // an object with itself. +bool +BranchFolder::MergePotentialsElt::operator<(const MergePotentialsElt &o) const { + if (getHash() < o.getHash()) + return true; + else if (getHash() > o.getHash()) + return false; + else if (getBlock()->getNumber() < o.getBlock()->getNumber()) + return true; + else if (getBlock()->getNumber() > o.getBlock()->getNumber()) + return false; + else { + // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing + // an object with itself. #ifndef _GLIBCXX_DEBUG - assert(0 && "Predecessor appears twice"); + llvm_unreachable("Predecessor appears twice"); #endif - return false; + return false; + } +} + +/// CountTerminators - Count the number of terminators in the given +/// block and set I to the position of the first non-terminator, if there +/// is one, or MBB->end() otherwise. +static unsigned CountTerminators(MachineBasicBlock *MBB, + MachineBasicBlock::iterator &I) { + I = MBB->end(); + unsigned NumTerms = 0; + for (;;) { + if (I == MBB->begin()) { + I = MBB->end(); + break; } + --I; + if (!I->getDesc().isTerminator()) break; + ++NumTerms; + } + return NumTerms; +} + +/// ProfitableToMerge - Check if two machine basic blocks have a common tail +/// and decide if it would be profitable to merge those tails. Return the +/// length of the common tail and iterators to the first common instruction +/// in each block. +static bool ProfitableToMerge(MachineBasicBlock *MBB1, + MachineBasicBlock *MBB2, + unsigned minCommonTailLength, + unsigned &CommonTailLen, + MachineBasicBlock::iterator &I1, + MachineBasicBlock::iterator &I2, + MachineBasicBlock *SuccBB, + MachineBasicBlock *PredBB) { + CommonTailLen = ComputeCommonTailLength(MBB1, MBB2, I1, I2); + MachineFunction *MF = MBB1->getParent(); + + if (CommonTailLen == 0) + return false; + + // It's almost always profitable to merge any number of non-terminator + // instructions with the block that falls through into the common successor. + if (MBB1 == PredBB || MBB2 == PredBB) { + MachineBasicBlock::iterator I; + unsigned NumTerms = CountTerminators(MBB1 == PredBB ? MBB2 : MBB1, I); + if (CommonTailLen > NumTerms) + return true; + } + + // If one of the blocks can be completely merged and happens to be in + // a position where the other could fall through into it, merge any number + // of instructions, because it can be done without a branch. + // TODO: If the blocks are not adjacent, move one of them so that they are? + if (MBB1->isLayoutSuccessor(MBB2) && I2 == MBB2->begin()) + return true; + if (MBB2->isLayoutSuccessor(MBB1) && I1 == MBB1->begin()) + return true; + + // If both blocks have an unconditional branch temporarily stripped out, + // count that as an additional common instruction for the following + // heuristics. + unsigned EffectiveTailLen = CommonTailLen; + if (SuccBB && MBB1 != PredBB && MBB2 != PredBB && + !MBB1->back().getDesc().isBarrier() && + !MBB2->back().getDesc().isBarrier()) + ++EffectiveTailLen; + + // Check if the common tail is long enough to be worthwhile. + if (EffectiveTailLen >= minCommonTailLength) + return true; + + // If we are optimizing for code size, 2 instructions in common is enough if + // we don't have to split a block. At worst we will be introducing 1 new + // branch instruction, which is likely to be smaller than the 2 + // instructions that would be deleted in the merge. + if (EffectiveTailLen >= 2 && + MF->getFunction()->hasFnAttr(Attribute::OptimizeForSize) && + (I1 == MBB1->begin() || I2 == MBB2->begin())) + return true; + + return false; } /// ComputeSameTails - Look through all the blocks in MergePotentials that have -/// hash CurHash (guaranteed to match the last element). Build the vector +/// hash CurHash (guaranteed to match the last element). Build the vector /// SameTails of all those that have the (same) largest number of instructions /// in common of any pair of these blocks. SameTails entries contain an -/// iterator into MergePotentials (from which the MachineBasicBlock can be -/// found) and a MachineBasicBlock::iterator into that MBB indicating the +/// iterator into MergePotentials (from which the MachineBasicBlock can be +/// found) and a MachineBasicBlock::iterator into that MBB indicating the /// instruction where the matching code sequence begins. /// Order of elements in SameTails is the reverse of the order in which /// those blocks appear in MergePotentials (where they are not necessarily /// consecutive). -unsigned BranchFolder::ComputeSameTails(unsigned CurHash, - unsigned minCommonTailLength) { +unsigned BranchFolder::ComputeSameTails(unsigned CurHash, + unsigned minCommonTailLength, + MachineBasicBlock *SuccBB, + MachineBasicBlock *PredBB) { unsigned maxCommonTailLength = 0U; SameTails.clear(); MachineBasicBlock::iterator TrialBBI1, TrialBBI2; MPIterator HighestMPIter = prior(MergePotentials.end()); for (MPIterator CurMPIter = prior(MergePotentials.end()), - B = MergePotentials.begin(); - CurMPIter!=B && CurMPIter->first==CurHash; + B = MergePotentials.begin(); + CurMPIter != B && CurMPIter->getHash() == CurHash; --CurMPIter) { - for (MPIterator I = prior(CurMPIter); I->first==CurHash ; --I) { - unsigned CommonTailLen = ComputeCommonTailLength( - CurMPIter->second, - I->second, - TrialBBI1, TrialBBI2); - // If we will have to split a block, there should be at least - // minCommonTailLength instructions in common; if not, at worst - // we will be replacing a fallthrough into the common tail with a - // branch, which at worst breaks even with falling through into - // the duplicated common tail, so 1 instruction in common is enough. - // We will always pick a block we do not have to split as the common - // tail if there is one. - // (Empty blocks will get forwarded and need not be considered.) - if (CommonTailLen >= minCommonTailLength || - (CommonTailLen > 0 && - (TrialBBI1==CurMPIter->second->begin() || - TrialBBI2==I->second->begin()))) { + for (MPIterator I = prior(CurMPIter); I->getHash() == CurHash ; --I) { + unsigned CommonTailLen; + if (ProfitableToMerge(CurMPIter->getBlock(), I->getBlock(), + minCommonTailLength, + CommonTailLen, TrialBBI1, TrialBBI2, + SuccBB, PredBB)) { if (CommonTailLen > maxCommonTailLength) { SameTails.clear(); maxCommonTailLength = CommonTailLen; HighestMPIter = CurMPIter; - SameTails.push_back(std::make_pair(CurMPIter, TrialBBI1)); + SameTails.push_back(SameTailElt(CurMPIter, TrialBBI1)); } if (HighestMPIter == CurMPIter && CommonTailLen == maxCommonTailLength) - SameTails.push_back(std::make_pair(I, TrialBBI2)); + SameTails.push_back(SameTailElt(I, TrialBBI2)); } - if (I==B) + if (I == B) break; } } @@ -523,95 +596,120 @@ unsigned BranchFolder::ComputeSameTails(unsigned CurHash, /// RemoveBlocksWithHash - Remove all blocks with hash CurHash from /// MergePotentials, restoring branches at ends of blocks as appropriate. -void BranchFolder::RemoveBlocksWithHash(unsigned CurHash, - MachineBasicBlock* SuccBB, - MachineBasicBlock* PredBB) { +void BranchFolder::RemoveBlocksWithHash(unsigned CurHash, + MachineBasicBlock *SuccBB, + MachineBasicBlock *PredBB) { MPIterator CurMPIter, B; - for (CurMPIter = prior(MergePotentials.end()), B = MergePotentials.begin(); - CurMPIter->first==CurHash; + for (CurMPIter = prior(MergePotentials.end()), B = MergePotentials.begin(); + CurMPIter->getHash() == CurHash; --CurMPIter) { // Put the unconditional branch back, if we need one. - MachineBasicBlock *CurMBB = CurMPIter->second; + MachineBasicBlock *CurMBB = CurMPIter->getBlock(); if (SuccBB && CurMBB != PredBB) FixTail(CurMBB, SuccBB, TII); - if (CurMPIter==B) + if (CurMPIter == B) break; } - if (CurMPIter->first!=CurHash) + if (CurMPIter->getHash() != CurHash) CurMPIter++; MergePotentials.erase(CurMPIter, MergePotentials.end()); } /// CreateCommonTailOnlyBlock - None of the blocks to be tail-merged consist /// only of the common tail. Create a block that does by splitting one. -unsigned BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB, - unsigned maxCommonTailLength) { - unsigned i, commonTailIndex; +bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB, + unsigned maxCommonTailLength, + unsigned &commonTailIndex) { + commonTailIndex = 0; unsigned TimeEstimate = ~0U; - for (i=0, commonTailIndex=0; isecond==PredBB) { + if (SameTails[i].getBlock() == PredBB) { commonTailIndex = i; break; } // Otherwise, make a (fairly bogus) choice based on estimate of // how long it will take the various blocks to execute. - unsigned t = EstimateRuntime(SameTails[i].first->second->begin(), - SameTails[i].second); - if (t<=TimeEstimate) { + unsigned t = EstimateRuntime(SameTails[i].getBlock()->begin(), + SameTails[i].getTailStartPos()); + if (t <= TimeEstimate) { TimeEstimate = t; commonTailIndex = i; } } - MachineBasicBlock::iterator BBI = SameTails[commonTailIndex].second; - MachineBasicBlock *MBB = SameTails[commonTailIndex].first->second; + MachineBasicBlock::iterator BBI = + SameTails[commonTailIndex].getTailStartPos(); + MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock(); - DOUT << "\nSplitting " << MBB->getNumber() << ", size " << - maxCommonTailLength; + // If the common tail includes any debug info we will take it pretty + // randomly from one of the inputs. Might be better to remove it? + DEBUG(dbgs() << "\nSplitting BB#" << MBB->getNumber() << ", size " + << maxCommonTailLength); MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI); - SameTails[commonTailIndex].first->second = newMBB; - SameTails[commonTailIndex].second = newMBB->begin(); + if (!newMBB) { + DEBUG(dbgs() << "... failed!"); + return false; + } + + SameTails[commonTailIndex].setBlock(newMBB); + SameTails[commonTailIndex].setTailStartPos(newMBB->begin()); + // If we split PredBB, newMBB is the new predecessor. - if (PredBB==MBB) + if (PredBB == MBB) PredBB = newMBB; - return commonTailIndex; + return true; } // See if any of the blocks in MergePotentials (which all have a common single // successor, or all have no successor) can be tail-merged. If there is a // successor, any blocks in MergePotentials that are not tail-merged and // are not immediately before Succ must have an unconditional branch to -// Succ added (but the predecessor/successor lists need no adjustment). +// Succ added (but the predecessor/successor lists need no adjustment). // The lone predecessor of Succ that falls through into Succ, // if any, is given in PredBB. -bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB, - MachineBasicBlock* PredBB) { - // It doesn't make sense to save a single instruction since tail merging - // will add a jump. - // FIXME: Ask the target to provide the threshold? - unsigned minCommonTailLength = (SuccBB ? 1 : 2) + 1; - MadeChange = false; - - DOUT << "\nTryMergeBlocks " << MergePotentials.size() << '\n'; +bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB, + MachineBasicBlock *PredBB) { + bool MadeChange = false; + + // Except for the special cases below, tail-merge if there are at least + // this many instructions in common. + unsigned minCommonTailLength = TailMergeSize; + + DEBUG(dbgs() << "\nTryTailMergeBlocks: "; + for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) + dbgs() << "BB#" << MergePotentials[i].getBlock()->getNumber() + << (i == e-1 ? "" : ", "); + dbgs() << "\n"; + if (SuccBB) { + dbgs() << " with successor BB#" << SuccBB->getNumber() << '\n'; + if (PredBB) + dbgs() << " which has fall-through from BB#" + << PredBB->getNumber() << "\n"; + } + dbgs() << "Looking for common tails of at least " + << minCommonTailLength << " instruction" + << (minCommonTailLength == 1 ? "" : "s") << '\n'; + ); // Sort by hash value so that blocks with identical end sequences sort // together. - std::stable_sort(MergePotentials.begin(), MergePotentials.end(),MergeCompare); + std::stable_sort(MergePotentials.begin(), MergePotentials.end()); // Walk through equivalence sets looking for actual exact matches. while (MergePotentials.size() > 1) { - unsigned CurHash = prior(MergePotentials.end())->first; - + unsigned CurHash = MergePotentials.back().getHash(); + // Build SameTails, identifying the set of blocks with this hash code // and with the maximum number of instructions in common. - unsigned maxCommonTailLength = ComputeSameTails(CurHash, - minCommonTailLength); + unsigned maxCommonTailLength = ComputeSameTails(CurHash, + minCommonTailLength, + SuccBB, PredBB); - // If we didn't find any pair that has at least minCommonTailLength + // If we didn't find any pair that has at least minCommonTailLength // instructions in common, remove all blocks with this hash code and retry. if (SameTails.empty()) { RemoveBlocksWithHash(CurHash, SuccBB, PredBB); @@ -622,38 +720,64 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB, // block, which we can't jump to), we can treat all blocks with this same // tail at once. Use PredBB if that is one of the possibilities, as that // will not introduce any extra branches. - MachineBasicBlock *EntryBB = MergePotentials.begin()->second-> - getParent()->begin(); - unsigned int commonTailIndex, i; - for (commonTailIndex=SameTails.size(), i=0; isecond; - if (MBB->begin() == SameTails[i].second && MBB != EntryBB) { - commonTailIndex = i; - if (MBB==PredBB) + MachineBasicBlock *EntryBB = MergePotentials.begin()->getBlock()-> + getParent()->begin(); + unsigned commonTailIndex = SameTails.size(); + // If there are two blocks, check to see if one can be made to fall through + // into the other. + if (SameTails.size() == 2 && + SameTails[0].getBlock()->isLayoutSuccessor(SameTails[1].getBlock()) && + SameTails[1].tailIsWholeBlock()) + commonTailIndex = 1; + else if (SameTails.size() == 2 && + SameTails[1].getBlock()->isLayoutSuccessor( + SameTails[0].getBlock()) && + SameTails[0].tailIsWholeBlock()) + commonTailIndex = 0; + else { + // Otherwise just pick one, favoring the fall-through predecessor if + // there is one. + for (unsigned i = 0, e = SameTails.size(); i != e; ++i) { + MachineBasicBlock *MBB = SameTails[i].getBlock(); + if (MBB == EntryBB && SameTails[i].tailIsWholeBlock()) + continue; + if (MBB == PredBB) { + commonTailIndex = i; break; + } + if (SameTails[i].tailIsWholeBlock()) + commonTailIndex = i; } } - if (commonTailIndex==SameTails.size()) { + if (commonTailIndex == SameTails.size() || + (SameTails[commonTailIndex].getBlock() == PredBB && + !SameTails[commonTailIndex].tailIsWholeBlock())) { // None of the blocks consist entirely of the common tail. // Split a block so that one does. - commonTailIndex = CreateCommonTailOnlyBlock(PredBB, maxCommonTailLength); + if (!CreateCommonTailOnlyBlock(PredBB, + maxCommonTailLength, commonTailIndex)) { + RemoveBlocksWithHash(CurHash, SuccBB, PredBB); + continue; + } } - MachineBasicBlock *MBB = SameTails[commonTailIndex].first->second; + MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock(); // MBB is common tail. Adjust all other BB's to jump to this one. // Traversal must be forwards so erases work. - DOUT << "\nUsing common tail " << MBB->getNumber() << " for "; - for (unsigned int i=0; igetNumber() + << " for "); + for (unsigned int i=0, e = SameTails.size(); i != e; ++i) { + if (commonTailIndex == i) continue; - DOUT << SameTails[i].first->second->getNumber() << ","; + DEBUG(dbgs() << "BB#" << SameTails[i].getBlock()->getNumber() + << (i == e-1 ? "" : ", ")); // Hack the end off BB i, making it jump to BB commonTailIndex instead. - ReplaceTailWithBranchTo(SameTails[i].second, MBB); + ReplaceTailWithBranchTo(SameTails[i].getTailStartPos(), MBB); // BB i is no longer a predecessor of SuccBB; remove it from the worklist. - MergePotentials.erase(SameTails[i].first); + MergePotentials.erase(SameTails[i].getMPIter()); } - DOUT << "\n"; + DEBUG(dbgs() << "\n"); // We leave commonTailIndex in the worklist in case there are other blocks // that match it with a smaller number of instructions. MadeChange = true; @@ -664,26 +788,27 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB, bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { if (!EnableTailMerge) return false; - - MadeChange = false; + + bool MadeChange = false; // First find blocks with no successors. MergePotentials.clear(); for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) { if (I->succ_empty()) - MergePotentials.push_back(std::make_pair(HashEndOfMBB(I, 2U), I)); + MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(I), I)); } + // See if we can do any tail merging on those. if (MergePotentials.size() < TailMergeThreshold && MergePotentials.size() >= 2) - MadeChange |= TryMergeBlocks(NULL, NULL); + MadeChange |= TryTailMergeBlocks(NULL, NULL); // Look at blocks (IBB) with multiple predecessors (PBB). // We change each predecessor to a canonical form, by // (1) temporarily removing any unconditional branch from the predecessor // to IBB, and // (2) alter conditional branches so they branch to the other block - // not IBB; this may require adding back an unconditional branch to IBB + // not IBB; this may require adding back an unconditional branch to IBB // later, where there wasn't one coming in. E.g. // Bcc IBB // fallthrough to QBB @@ -697,17 +822,22 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { // a compile-time infinite loop repeatedly doing and undoing the same // transformations.) - for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) { + for (MachineFunction::iterator I = llvm::next(MF.begin()), E = MF.end(); + I != E; ++I) { if (I->pred_size() >= 2 && I->pred_size() < TailMergeThreshold) { + SmallPtrSet UniquePreds; MachineBasicBlock *IBB = I; MachineBasicBlock *PredBB = prior(I); MergePotentials.clear(); - for (MachineBasicBlock::pred_iterator P = I->pred_begin(), + for (MachineBasicBlock::pred_iterator P = I->pred_begin(), E2 = I->pred_end(); P != E2; ++P) { - MachineBasicBlock* PBB = *P; + MachineBasicBlock *PBB = *P; // Skip blocks that loop to themselves, can't tail merge these. - if (PBB==IBB) + if (PBB == IBB) + continue; + // Visit each predecessor only once. + if (!UniquePreds.insert(PBB)) continue; MachineBasicBlock *TBB = 0, *FBB = 0; SmallVector Cond; @@ -715,53 +845,54 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { // Failing case: IBB is the target of a cbr, and // we cannot reverse the branch. SmallVector NewCond(Cond); - if (!Cond.empty() && TBB==IBB) { + if (!Cond.empty() && TBB == IBB) { if (TII->ReverseBranchCondition(NewCond)) continue; // This is the QBB case described above if (!FBB) - FBB = next(MachineFunction::iterator(PBB)); + FBB = llvm::next(MachineFunction::iterator(PBB)); } // Failing case: the only way IBB can be reached from PBB is via // exception handling. Happens for landing pads. Would be nice // to have a bit in the edge so we didn't have to do all this. if (IBB->isLandingPad()) { MachineFunction::iterator IP = PBB; IP++; - MachineBasicBlock* PredNextBB = NULL; - if (IP!=MF.end()) + MachineBasicBlock *PredNextBB = NULL; + if (IP != MF.end()) PredNextBB = IP; - if (TBB==NULL) { - if (IBB!=PredNextBB) // fallthrough + if (TBB == NULL) { + if (IBB != PredNextBB) // fallthrough continue; } else if (FBB) { - if (TBB!=IBB && FBB!=IBB) // cbr then ubr + if (TBB != IBB && FBB != IBB) // cbr then ubr continue; } else if (Cond.empty()) { - if (TBB!=IBB) // ubr + if (TBB != IBB) // ubr continue; } else { - if (TBB!=IBB && IBB!=PredNextBB) // cbr + if (TBB != IBB && IBB != PredNextBB) // cbr continue; } } // Remove the unconditional branch at the end, if any. if (TBB && (Cond.empty() || FBB)) { + DebugLoc dl; // FIXME: this is nowhere TII->RemoveBranch(*PBB); if (!Cond.empty()) // reinsert conditional branch only, for now - TII->InsertBranch(*PBB, (TBB==IBB) ? FBB : TBB, 0, NewCond); + TII->InsertBranch(*PBB, (TBB == IBB) ? FBB : TBB, 0, NewCond, dl); } - MergePotentials.push_back(std::make_pair(HashEndOfMBB(PBB, 1U), *P)); + MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(PBB), *P)); } } - if (MergePotentials.size() >= 2) - MadeChange |= TryMergeBlocks(I, PredBB); - // Reinsert an unconditional branch if needed. - // The 1 below can occur as a result of removing blocks in TryMergeBlocks. - PredBB = prior(I); // this may have been changed in TryMergeBlocks - if (MergePotentials.size()==1 && - MergePotentials.begin()->second != PredBB) - FixTail(MergePotentials.begin()->second, I, TII); + if (MergePotentials.size() >= 2) + MadeChange |= TryTailMergeBlocks(IBB, PredBB); + // Reinsert an unconditional branch if needed. + // The 1 below can occur as a result of removing blocks in TryTailMergeBlocks. + PredBB = prior(I); // this may have been changed in TryTailMergeBlocks + if (MergePotentials.size() == 1 && + MergePotentials.begin()->getBlock() != PredBB) + FixTail(MergePotentials.begin()->getBlock(), IBB, TII); } } return MadeChange; @@ -772,15 +903,15 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { //===----------------------------------------------------------------------===// bool BranchFolder::OptimizeBranches(MachineFunction &MF) { - MadeChange = false; - + bool MadeChange = false; + // Make sure blocks are numbered in order MF.RenumberBlocks(); for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) { MachineBasicBlock *MBB = I++; - OptimizeBlock(MBB); - + MadeChange |= OptimizeBlock(MBB); + // If it is dead, remove it. if (MBB->pred_empty()) { RemoveDeadBlock(MBB); @@ -791,100 +922,78 @@ bool BranchFolder::OptimizeBranches(MachineFunction &MF) { return MadeChange; } - -/// CanFallThrough - Return true if the specified block (with the specified -/// branch condition) can implicitly transfer control to the block after it by -/// falling off the end of it. This should return false if it can reach the -/// block after it, but it uses an explicit branch to do so (e.g. a table jump). -/// -/// True is a conservative answer. -/// -bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB, - bool BranchUnAnalyzable, - MachineBasicBlock *TBB, - MachineBasicBlock *FBB, - const SmallVectorImpl &Cond) { - MachineFunction::iterator Fallthrough = CurBB; - ++Fallthrough; - // If FallthroughBlock is off the end of the function, it can't fall through. - if (Fallthrough == CurBB->getParent()->end()) - return false; - - // If FallthroughBlock isn't a successor of CurBB, no fallthrough is possible. - if (!CurBB->isSuccessor(Fallthrough)) - return false; - - // If we couldn't analyze the branch, assume it could fall through. - if (BranchUnAnalyzable) return true; - - // If there is no branch, control always falls through. - if (TBB == 0) return true; - - // If there is some explicit branch to the fallthrough block, it can obviously - // reach, even though the branch should get folded to fall through implicitly. - if (MachineFunction::iterator(TBB) == Fallthrough || - MachineFunction::iterator(FBB) == Fallthrough) +// Blocks should be considered empty if they contain only debug info; +// else the debug info would affect codegen. +static bool IsEmptyBlock(MachineBasicBlock *MBB) { + if (MBB->empty()) return true; - - // If it's an unconditional branch to some block not the fall through, it - // doesn't fall through. - if (Cond.empty()) return false; - - // Otherwise, if it is conditional and has no explicit false block, it falls - // through. - return FBB == 0; + for (MachineBasicBlock::iterator MBBI = MBB->begin(), MBBE = MBB->end(); + MBBI!=MBBE; ++MBBI) { + if (!MBBI->isDebugValue()) + return false; + } + return true; } -/// CanFallThrough - Return true if the specified can implicitly transfer -/// control to the block after it by falling off the end of it. This should -/// return false if it can reach the block after it, but it uses an explicit -/// branch to do so (e.g. a table jump). -/// -/// True is a conservative answer. -/// -bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB) { - MachineBasicBlock *TBB = 0, *FBB = 0; - SmallVector Cond; - bool CurUnAnalyzable = TII->AnalyzeBranch(*CurBB, TBB, FBB, Cond, true); - return CanFallThrough(CurBB, CurUnAnalyzable, TBB, FBB, Cond); +// Blocks with only debug info and branches should be considered the same +// as blocks with only branches. +static bool IsBranchOnlyBlock(MachineBasicBlock *MBB) { + MachineBasicBlock::iterator MBBI, MBBE; + for (MBBI = MBB->begin(), MBBE = MBB->end(); MBBI!=MBBE; ++MBBI) { + if (!MBBI->isDebugValue()) + break; + } + return (MBBI->getDesc().isBranch()); } /// IsBetterFallthrough - Return true if it would be clearly better to /// fall-through to MBB1 than to fall through into MBB2. This has to return /// a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will /// result in infinite loops. -static bool IsBetterFallthrough(MachineBasicBlock *MBB1, +static bool IsBetterFallthrough(MachineBasicBlock *MBB1, MachineBasicBlock *MBB2) { // Right now, we use a simple heuristic. If MBB2 ends with a call, and // MBB1 doesn't, we prefer to fall through into MBB1. This allows us to // optimize branches that branch to either a return block or an assert block // into a fallthrough to the return. - if (MBB1->empty() || MBB2->empty()) return false; - + if (IsEmptyBlock(MBB1) || IsEmptyBlock(MBB2)) return false; + // If there is a clear successor ordering we make sure that one block // will fall through to the next if (MBB1->isSuccessor(MBB2)) return true; if (MBB2->isSuccessor(MBB1)) return false; - MachineInstr *MBB1I = --MBB1->end(); - MachineInstr *MBB2I = --MBB2->end(); + // Neither block consists entirely of debug info (per IsEmptyBlock check), + // so we needn't test for falling off the beginning here. + MachineBasicBlock::iterator MBB1I = --MBB1->end(); + while (MBB1I->isDebugValue()) + --MBB1I; + MachineBasicBlock::iterator MBB2I = --MBB2->end(); + while (MBB2I->isDebugValue()) + --MBB2I; return MBB2I->getDesc().isCall() && !MBB1I->getDesc().isCall(); } /// OptimizeBlock - Analyze and optimize control flow related to the specified /// block. This is never called on the entry block. -void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { +bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { + bool MadeChange = false; + MachineFunction &MF = *MBB->getParent(); + DebugLoc dl; // FIXME: this is nowhere +ReoptimizeBlock: + MachineFunction::iterator FallThrough = MBB; ++FallThrough; - + // If this block is empty, make everyone use its fall-through, not the block // explicitly. Landing pads should not do this since the landing-pad table - // points to this block. - if (MBB->empty() && !MBB->isLandingPad()) { + // points to this block. Blocks with their addresses taken shouldn't be + // optimized away. + if (IsEmptyBlock(MBB) && !MBB->isLandingPad() && !MBB->hasAddressTaken()) { // Dead block? Leave for cleanup later. - if (MBB->pred_empty()) return; - - if (FallThrough == MBB->getParent()->end()) { + if (MBB->pred_empty()) return MadeChange; + + if (FallThrough == MF.end()) { // TODO: Simplify preds to not branch here if possible! } else { // Rewrite all predecessors of the old block to go to the fallthrough @@ -893,14 +1002,13 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { MachineBasicBlock *Pred = *(MBB->pred_end()-1); Pred->ReplaceUsesOfBlockWith(MBB, FallThrough); } - // If MBB was the target of a jump table, update jump tables to go to the // fallthrough instead. - MBB->getParent()->getJumpTableInfo()-> - ReplaceMBBInJumpTables(MBB, FallThrough); + if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo()) + MJTI->ReplaceMBBInJumpTables(MBB, FallThrough); MadeChange = true; } - return; + return MadeChange; } // Check to see if we can simplify the terminator of the block before this @@ -915,39 +1023,59 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { // If the CFG for the prior block has extra edges, remove them. MadeChange |= PrevBB.CorrectExtraCFGEdges(PriorTBB, PriorFBB, !PriorCond.empty()); - + // If the previous branch is conditional and both conditions go to the same // destination, remove the branch, replacing it with an unconditional one or // a fall-through. if (PriorTBB && PriorTBB == PriorFBB) { TII->RemoveBranch(PrevBB); - PriorCond.clear(); + PriorCond.clear(); if (PriorTBB != MBB) - TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond); + TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond, dl); MadeChange = true; ++NumBranchOpts; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } - + + // If the previous block unconditionally falls through to this block and + // this block has no other predecessors, move the contents of this block + // into the prior block. This doesn't usually happen when SimplifyCFG + // has been used, but it can happen if tail merging splits a fall-through + // predecessor of a block. + // This has to check PrevBB->succ_size() because EH edges are ignored by + // AnalyzeBranch. + if (PriorCond.empty() && !PriorTBB && MBB->pred_size() == 1 && + PrevBB.succ_size() == 1 && + !MBB->hasAddressTaken()) { + DEBUG(dbgs() << "\nMerging into block: " << PrevBB + << "From MBB: " << *MBB); + PrevBB.splice(PrevBB.end(), MBB, MBB->begin(), MBB->end()); + PrevBB.removeSuccessor(PrevBB.succ_begin());; + assert(PrevBB.succ_empty()); + PrevBB.transferSuccessors(MBB); + MadeChange = true; + return MadeChange; + } + // If the previous branch *only* branches to *this* block (conditional or // not) remove the branch. if (PriorTBB == MBB && PriorFBB == 0) { TII->RemoveBranch(PrevBB); MadeChange = true; ++NumBranchOpts; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } - + // If the prior block branches somewhere else on the condition and here if // the condition is false, remove the uncond second branch. if (PriorFBB == MBB) { TII->RemoveBranch(PrevBB); - TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond); + TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond, dl); MadeChange = true; ++NumBranchOpts; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } - + // If the prior block branches here on true and somewhere else on false, and // if the branch condition is reversible, reverse the branch to create a // fall-through. @@ -955,71 +1083,55 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { SmallVector NewPriorCond(PriorCond); if (!TII->ReverseBranchCondition(NewPriorCond)) { TII->RemoveBranch(PrevBB); - TII->InsertBranch(PrevBB, PriorFBB, 0, NewPriorCond); + TII->InsertBranch(PrevBB, PriorFBB, 0, NewPriorCond, dl); MadeChange = true; ++NumBranchOpts; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } } - - // If this block doesn't fall through (e.g. it ends with an uncond branch or - // has no successors) and if the pred falls through into this block, and if - // it would otherwise fall through into the block after this, move this - // block to the end of the function. + + // If this block has no successors (e.g. it is a return block or ends with + // a call to a no-return function like abort or __cxa_throw) and if the pred + // falls through into this block, and if it would otherwise fall through + // into the block after this, move this block to the end of the function. // // We consider it more likely that execution will stay in the function (e.g. // due to loops) than it is to exit it. This asserts in loops etc, moving // the assert condition out of the loop body. - if (!PriorCond.empty() && PriorFBB == 0 && + if (MBB->succ_empty() && !PriorCond.empty() && PriorFBB == 0 && MachineFunction::iterator(PriorTBB) == FallThrough && - !CanFallThrough(MBB)) { + !MBB->canFallThrough()) { bool DoTransform = true; - + // We have to be careful that the succs of PredBB aren't both no-successor // blocks. If neither have successors and if PredBB is the second from // last block in the function, we'd just keep swapping the two blocks for // last. Only do the swap if one is clearly better to fall through than // the other. - if (FallThrough == --MBB->getParent()->end() && + if (FallThrough == --MF.end() && !IsBetterFallthrough(PriorTBB, MBB)) DoTransform = false; - // We don't want to do this transformation if we have control flow like: - // br cond BB2 - // BB1: - // .. - // jmp BBX - // BB2: - // .. - // ret - // - // In this case, we could actually be moving the return block *into* a - // loop! - if (DoTransform && !MBB->succ_empty() && - (!CanFallThrough(PriorTBB) || PriorTBB->empty())) - DoTransform = false; - - if (DoTransform) { // Reverse the branch so we will fall through on the previous true cond. SmallVector NewPriorCond(PriorCond); if (!TII->ReverseBranchCondition(NewPriorCond)) { - DOUT << "\nMoving MBB: " << *MBB; - DOUT << "To make fallthrough to: " << *PriorTBB << "\n"; - + DEBUG(dbgs() << "\nMoving MBB: " << *MBB + << "To make fallthrough to: " << *PriorTBB << "\n"); + TII->RemoveBranch(PrevBB); - TII->InsertBranch(PrevBB, MBB, 0, NewPriorCond); + TII->InsertBranch(PrevBB, MBB, 0, NewPriorCond, dl); // Move this block to the end of the function. - MBB->moveAfter(--MBB->getParent()->end()); + MBB->moveAfter(--MF.end()); MadeChange = true; ++NumBranchOpts; - return; + return MadeChange; } } } } - + // Analyze the branch in the current block. MachineBasicBlock *CurTBB = 0, *CurFBB = 0; SmallVector CurCond; @@ -1028,7 +1140,7 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { // If the CFG for the prior block has extra edges, remove them. MadeChange |= MBB->CorrectExtraCFGEdges(CurTBB, CurFBB, !CurCond.empty()); - // If this is a two-way branch, and the FBB branches to this block, reverse + // If this is a two-way branch, and the FBB branches to this block, reverse // the condition so the single-basic-block loop is faster. Instead of: // Loop: xxx; jcc Out; jmp Loop // we want: @@ -1037,35 +1149,51 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { SmallVector NewCond(CurCond); if (!TII->ReverseBranchCondition(NewCond)) { TII->RemoveBranch(*MBB); - TII->InsertBranch(*MBB, CurFBB, CurTBB, NewCond); + TII->InsertBranch(*MBB, CurFBB, CurTBB, NewCond, dl); MadeChange = true; ++NumBranchOpts; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } } - - + // If this branch is the only thing in its block, see if we can forward // other blocks across it. - if (CurTBB && CurCond.empty() && CurFBB == 0 && - MBB->begin()->getDesc().isBranch() && CurTBB != MBB) { + if (CurTBB && CurCond.empty() && CurFBB == 0 && + IsBranchOnlyBlock(MBB) && CurTBB != MBB && + !MBB->hasAddressTaken()) { // This block may contain just an unconditional branch. Because there can // be 'non-branch terminators' in the block, try removing the branch and // then seeing if the block is empty. TII->RemoveBranch(*MBB); - + // If the only things remaining in the block are debug info, remove these + // as well, so this will behave the same as an empty block in non-debug + // mode. + if (!MBB->empty()) { + bool NonDebugInfoFound = false; + for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); + I != E; ++I) { + if (!I->isDebugValue()) { + NonDebugInfoFound = true; + break; + } + } + if (!NonDebugInfoFound) + // Make the block empty, losing the debug info (we could probably + // improve this in some cases.) + MBB->erase(MBB->begin(), MBB->end()); + } // If this block is just an unconditional branch to CurTBB, we can // usually completely eliminate the block. The only case we cannot // completely eliminate the block is when the block before this one // falls through into MBB and we can't understand the prior block's branch // condition. if (MBB->empty()) { - bool PredHasNoFallThrough = TII->BlockHasNoFallThrough(PrevBB); + bool PredHasNoFallThrough = !PrevBB.canFallThrough(); if (PredHasNoFallThrough || !PriorUnAnalyzable || !PrevBB.isSuccessor(MBB)) { // If the prior block falls through into us, turn it into an // explicit branch to us to make updates simpler. - if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) && + if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) && PriorTBB != MBB && PriorFBB != MBB) { if (PriorTBB == 0) { assert(PriorCond.empty() && PriorFBB == 0 && @@ -1076,7 +1204,7 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { PriorFBB = MBB; } TII->RemoveBranch(PrevBB); - TII->InsertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond); + TII->InsertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, dl); } // Iterate through all the predecessors, revectoring each in-turn. @@ -1092,34 +1220,48 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { } else { DidChange = true; PMBB->ReplaceUsesOfBlockWith(MBB, CurTBB); + // If this change resulted in PMBB ending in a conditional + // branch where both conditions go to the same destination, + // change this to an unconditional branch (and fix the CFG). + MachineBasicBlock *NewCurTBB = 0, *NewCurFBB = 0; + SmallVector NewCurCond; + bool NewCurUnAnalyzable = TII->AnalyzeBranch(*PMBB, NewCurTBB, + NewCurFBB, NewCurCond, true); + if (!NewCurUnAnalyzable && NewCurTBB && NewCurTBB == NewCurFBB) { + TII->RemoveBranch(*PMBB); + NewCurCond.clear(); + TII->InsertBranch(*PMBB, NewCurTBB, 0, NewCurCond, dl); + MadeChange = true; + ++NumBranchOpts; + PMBB->CorrectExtraCFGEdges(NewCurTBB, 0, false); + } } } // Change any jumptables to go to the new MBB. - MBB->getParent()->getJumpTableInfo()-> - ReplaceMBBInJumpTables(MBB, CurTBB); + if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo()) + MJTI->ReplaceMBBInJumpTables(MBB, CurTBB); if (DidChange) { ++NumBranchOpts; MadeChange = true; - if (!HasBranchToSelf) return; + if (!HasBranchToSelf) return MadeChange; } } } - + // Add the branch back if the block is more than just an uncond branch. - TII->InsertBranch(*MBB, CurTBB, 0, CurCond); + TII->InsertBranch(*MBB, CurTBB, 0, CurCond, dl); } } // If the prior block doesn't fall through into this block, and if this // block doesn't fall through into some other block, see if we can find a // place to move this block where a fall-through will happen. - if (!CanFallThrough(&PrevBB, PriorUnAnalyzable, - PriorTBB, PriorFBB, PriorCond)) { + if (!PrevBB.canFallThrough()) { + // Now we know that there was no fall-through into this block, check to // see if it has a fall-through into its successor. - bool CurFallsThru = CanFallThrough(MBB, CurUnAnalyzable, CurTBB, CurFBB, - CurCond); + bool CurFallsThru = MBB->canFallThrough(); if (!MBB->isLandingPad()) { // Check all the predecessors of this block. If one of them has no fall @@ -1129,12 +1271,15 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { // Analyze the branch at the end of the pred. MachineBasicBlock *PredBB = *PI; MachineFunction::iterator PredFallthrough = PredBB; ++PredFallthrough; - if (PredBB != MBB && !CanFallThrough(PredBB) + MachineBasicBlock *PredTBB = 0, *PredFBB = 0; + SmallVector PredCond; + if (PredBB != MBB && !PredBB->canFallThrough() && + !TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true) && (!CurFallsThru || !CurTBB || !CurFBB) && (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) { // If the current block doesn't fall through, just move it. // If the current block can fall through and does not end with a - // conditional branch, we need to append an unconditional jump to + // conditional branch, we need to append an unconditional jump to // the (current) next block. To avoid a possible compile-time // infinite loop, move blocks only backward in this case. // Also, if there are already 2 branches here, we cannot add a third; @@ -1143,17 +1288,17 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { // B elsewhere // next: if (CurFallsThru) { - MachineBasicBlock *NextBB = next(MachineFunction::iterator(MBB)); + MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(MBB)); CurCond.clear(); - TII->InsertBranch(*MBB, NextBB, 0, CurCond); + TII->InsertBranch(*MBB, NextBB, 0, CurCond, dl); } MBB->moveAfter(PredBB); MadeChange = true; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } } } - + if (!CurFallsThru) { // Check all successors to see if we can move this block before it. for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(), @@ -1161,29 +1306,34 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { // Analyze the branch at the end of the block before the succ. MachineBasicBlock *SuccBB = *SI; MachineFunction::iterator SuccPrev = SuccBB; --SuccPrev; - std::vector SuccPrevCond; - + // If this block doesn't already fall-through to that successor, and if // the succ doesn't already have a block that can fall through into it, // and if the successor isn't an EH destination, we can arrange for the // fallthrough to happen. - if (SuccBB != MBB && !CanFallThrough(SuccPrev) && + if (SuccBB != MBB && &*SuccPrev != MBB && + !SuccPrev->canFallThrough() && !CurUnAnalyzable && !SuccBB->isLandingPad()) { MBB->moveBefore(SuccBB); MadeChange = true; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } } - + // Okay, there is no really great place to put this block. If, however, // the block before this one would be a fall-through if this block were // removed, move this block to the end of the function. - if (FallThrough != MBB->getParent()->end() && + MachineBasicBlock *PrevTBB = 0, *PrevFBB = 0; + SmallVector PrevCond; + if (FallThrough != MF.end() && + !TII->AnalyzeBranch(PrevBB, PrevTBB, PrevFBB, PrevCond, true) && PrevBB.isSuccessor(FallThrough)) { - MBB->moveAfter(--MBB->getParent()->end()); + MBB->moveAfter(--MF.end()); MadeChange = true; - return; + return MadeChange; } } } + + return MadeChange; }